Turbo-machinery, in general, can experience non-synchronous vibration (NSV). NSV is usually associated with an unstable rotor-bearing system mode, however, in many cases, a limit cycle is reached, which limits the amplitude of NSV. Large amplitude or unbound NSV can result in excessive vibration/noise and/or destruction of the turbo-machinery. NSV which is low frequency (typically lower than the synchronous speed of the machine) can result in undesirable noise.
NSV can be the result of many design parameters. Control of these parameters is not always easy, and in some cases unavoidable due to basic design requirements of a particular turbo-machine. In many instances, NSV control is accomplished by modifying rotor supports or optimization of the supports, often at increased cost, complexity or reduced component tolerance. However, these efforts often do not fully suppress NSV.
Full suppression of NSV for turbochargers that must operate over a large range of speeds, temperatures and external loading is seldom achieved. Depending on design, a turbocharger rotor may be mounted using floating ring bearings or partial floating ring bearings, which have clearances that allow for rotor drop (e.g., due to gravity). A designer typically needs to balance: (i) bearing clearance for rotor stability (minimization of NSV), (ii) rotor clearances for performance and (iii) turbocharger operability. To balance these factors, the operating envelope of the bearings (clearances, oil temperature range, oil type) requires extensive testing to verify that NSV is controlled. However, testing cannot always account for minor changes in bearing clearance due to wear, which can lead to NSV on turbochargers.
Another drawback of conventional turbocharger bearing systems is the large amount of lubricant required for a semi-floating ring bearing supported by a squeeze film damper (SFD) or a ball bearing supported by a SFD (noting that for a fully-floating ring, a lubricant layer lubricates rotation of the ring with respect to a surrounding support structure). SFD systems typically have open mounts that increase lubricant supply requirements to achieve optimum performance. In an alternative “closed” mount approach, sealing and re-use of lubricant results in a reduction of the lubricant required by a turbocharger; which in turn allows for use of a smaller lubricant pump for the engine. Such an approach also leads to an overall reduction in parasitic losses—leading to higher performance vehicles which are more fuel efficient.
Overall, a need exists for bearing technologies that address issues like noise, wear and performance. Various exemplary bearing components and housings presented herein can address such issues.